1. Field of the Invention
This invention relates to an apparatus mounted on a vehicle for detecting a condition of a road surface while the vehicle is traveling.
2. Description of the Related Art
U.S. Pat. No. 5,719,565 corresponding to Japanese patent application publication number 9-20223 discloses an apparatus mounted on a vehicle for detecting a condition of a road surface while the vehicle is traveling. In the apparatus of U.S. Pat. No. 5,719,565, the speeds of wheels of the vehicle are calculated based on wheel speed signals from wheel speed sensors. The accelerations of the wheels are calculated based on the calculated wheel speeds. High frequency components of the calculated wheel accelerations are filtered using high-pass filters to obtain the frequency components of the wheel accelerations which are due only to the road-surface condition. A variance among a limited number of temporally-spaced samples of each filtering-resultant wheel acceleration is calculated, and a determination is made as to whether or not the road-surface condition is bad by referring to the calculated variance. Specifically, when the calculated variance is equal to or greater than a reference value, it is determined that the road-surface condition is bad.
A typical wheel speed sensor includes a rotor which rotates together with a related vehicle wheel. The rotor has teeth. The typical sensor also includes a fixed portion for sensing every projection or every groove in the rotor teeth and thereby generating a wheel speed signal during the rotation of the rotor. In the case where the typical sensor is used by the apparatus of U.S. Pat. No. 5,719,565, a variation in shape and position among the projections or the grooves in the rotor teeth affects the calculated variance. Thus, the variation in shape and position among the projections or the grooves in the rotor teeth lowers the accuracy of the determination as to whether or not the road-surface condition is bad.
Japanese patent application publication number 6-80044 discloses an apparatus mounted on a vehicle for detecting a condition of a road surface while the vehicle is traveling. In the apparatus of Japanese application 6-80044, vehicle wheel speed data are derived from the output signal of a vehicle wheel speed sensor. A differential value of the vehicle wheel speed data is calculated for every unit time. Factors of a sequence of samples of data representing the calculated differential values are calculated as feature quantities related to the vehicle wheel speed. Specifically, with respect to the sample sequence, a mean amplitude, a relative amplitude variation, a histogram variance, and the number of data pieces in an amplitude value specified interval are calculated for every unit time. A fuzzy inference is implemented while the calculated feature quantities are used as input parameters. A determination is made as to whether the road-surface condition is good or bad on the basis of the result of the fuzzy inference.
U.S. Pat. No. 5,760,682 corresponding to Japanese patent application publication number 10-258618 discloses a method for detecting a deflated tire on a vehicle. In the method of U.S. Pat. No. 5,760,682, wheel speed values for each of four wheels are collected and analyzed for a statistical variation which would indicate low tire pressure. Prior to analysis, and following reset of the system, calibration factors are determined for each of the wheels to compensate rolling radius variations, and subsequently used to correct all wheel speed values. The corrected speed values are then filtered to exclude values which represent wheel slippage, rough road fluctuations, vehicle cornering, and uphill or downhill travel. When a sufficient number of values have been collected, an F-value is calculated substantially according to the statistical method xe2x80x9canalysis of the variancexe2x80x9d, and the F-value is compared to an empirically determined value corresponding to a predetermined pressure loss. This comparison can provide the basis for a driver warning. Since a larger F-value indicates a larger statistical difference in wheel speeds, the value can be rechecked after a further interval for additional pressure loss.
U.S. Pat. No. 4,651,290 corresponding to Japanese patent application publication number 6-318297 discloses an apparatus mounted on a vehicle for detecting a condition of a road surface while the vehicle is traveling. In the apparatus of U.S. Pat. No. 4,651,290, the speed of a wheel of the vehicle is calculated based on the output signal of a wheel speed sensor. The acceleration of the wheel is calculated based on the calculated wheel speed. The performance criterion of the road-surface condition is computed based on the calculated wheel acceleration. The computed performance criterion is compared with a setting value to determine wether the road-surface condition is good or bad. A first example of the performance criterion depends on a variance among a predetermined number of temporally-spaced samples of the wheel acceleration. A second example of the performance criterion depends on the number of samples of the wheel acceleration which exceed a reference value for every predetermined time interval. A third example of the performance criterion depends on the difference between the maximum and the minimum among the values indicated by temporally-spaced samples of the wheel acceleration for every predetermined time interval.
Japanese patent application publication number 5-126571 discloses an apparatus mounted on a vehicle for measuring the shape of a road surface. The apparatus of Japanese application 5-126571 includes a distance detector for detecting the distance between the road surface and a main body of the vehicle. The apparatus also includes an acceleration detector for detecting the vertical acceleration of the main body of the vehicle. The detected vertical acceleration is integrated on a second-order basis to calculate the amount of vertical vibration of the main body of the vehicle for every time interval corresponding to a predetermined distance traveled by the vehicle. The detected distance between the road surface and the main body of the vehicle is corrected in response to the calculated amount of vertical vibration. The shape of the road surface is detected on the basis of the correction resultant distance.
It is an object of this invention to provide an apparatus for accurately detecting a condition of a road surface even in the case where there is a variation in shape and position among the projections or the grooves in teeth of a rotor of a wheel speed sensor.
A first aspect of this invention provides an apparatus for detecting a condition of a road surface. The apparatus comprises vehicle wheel speed detecting means for outputting a vehicle wheel speed signal representing a speed of a wheel of a vehicle; vehicle wheel speed summating means for summating variations in the vehicle wheel speed represented by the vehicle wheel speed signal during every time period corresponding to one revolution of the vehicle wheel, and for generating a summation value representing a result of said summating; and road-surface condition detecting means for detecting a road-surface condition on the basis of a difference between a current summation value and a previous summation value generated by the vehicle wheel speed summating means.
A second aspect of this invention is based on the first aspect thereof, and provides an apparatus further comprising vehicle wheel acceleration calculating means for calculating an acceleration of the vehicle wheel from the vehicle wheel speed signal outputted from the vehicle wheel speed detecting means; and means provided in the vehicle wheel speed summating means for summating variations in the vehicle wheel acceleration calculated by the vehicle wheel acceleration calculating means, and for using a result of summating the variations in the vehicle wheel acceleration as a result of summating the variations in the vehicle wheel speed.
A third aspect of this invention is based on the first aspect thereof, and provides an apparatus further comprising vehicle wheel acceleration calculating means for calculating an acceleration of the vehicle wheel from the vehicle wheel speed signal outputted from the vehicle wheel speed detecting means; variance calculating means for calculating a variance of the vehicle wheel acceleration calculated by the vehicle wheel acceleration calculating means; and means provided in the vehicle wheel speed summating means for using the variance calculated by the variance calculating means as a result of summating the variations in the vehicle wheel speed.
A fourth aspect of this invention is based on the first aspect thereof, and provides an apparatus further comprising acceleration differential value calculating means for calculating a differential value of an acceleration of the vehicle wheel from the vehicle wheel speed signal outputted from the vehicle wheel speed detecting means; and means provided in the vehicle wheel speed summating means for summating variations in the differential value calculated by the acceleration differential value calculating means, and for using a result of summating the variations in the differential value as a result of summating the variations in the vehicle wheel speed.
A fifth aspect of this invention provides an apparatus for detecting a condition of a road surface. The apparatus comprises vehicle wheel speed detecting means for outputting a vehicle wheel speed signal representing a speed of a wheel of a vehicle; learning means for learning a variation in the vehicle wheel speed represented by the vehicle wheel speed signal outputted from the vehicle wheel speed detecting means, and for generating a learning-resultant value representing a result of said learning; and road-surface condition detecting means for detecting a road-surface condition on the basis of a difference between the learning-resultant value and a variation in the vehicle wheel speed represented by the vehicle wheel speed signal outputted from the vehicle wheel speed detecting means.
A sixth aspect of this invention is based on the fifth aspect thereof, and provides an apparatus wherein the learning means comprises means for extracting components from the variation in the vehicle wheel speed which are caused by a variation in rotor manufacture accuracy, and means for learning the extracted components of the variation in the vehicle wheel speed which are caused by a variation in rotor manufacture accuracy.
A seventh aspect of this invention is based on the fifth aspect thereof, and provides an apparatus wherein the learning means comprises means for learning an average of a value of summation of variations in the vehicle wheel speed.
An eighth aspect of this invention is based on the fifth aspect thereof, and provides an apparatus further comprising vehicle wheel acceleration calculating means for calculating an acceleration of the vehicle wheel from the vehicle wheel speed signal outputted from the vehicle wheel speed detecting means; means provided in the learning means for learning a variation in the vehicle wheel acceleration calculated by the vehicle wheel acceleration calculating means, and for using a result of learning the variation in the vehicle wheel acceleration as the learning-resultant value representing the result of learning the variation in the vehicle wheel speed; and means provided in the road-surface condition detecting means for detecting the road-surface condition on the basis of a difference between the learning-resultant value and a variation in the vehicle wheel acceleration calculated by the vehicle wheel acceleration calculating means.
A ninth aspect of this invention is based on the fifth aspect thereof, and provides an apparatus further comprising vehicle wheel acceleration calculating means for calculating an acceleration of the vehicle wheel from the vehicle wheel speed signal outputted from the vehicle wheel speed detecting means; variance calculating means for calculating a variance of the vehicle wheel acceleration calculated by the vehicle wheel acceleration calculating means; means provided in the learning means for learning a variation in the variance calculated by the variance calculating means, and for using a result of learning the variation in the variance as the learning-resultant value representing the result of learning the variation in the vehicle wheel speed; and means provided in the road-surface condition detecting means for detecting the road-surface condition on the basis of a difference between the learning-resultant value and a variation in the variance calculated by the variance calculating means.
A tenth aspect of this invention is based on the fifth aspect thereof, and provides an apparatus further comprising acceleration differential value calculating means for calculating a differential value of an acceleration of the vehicle wheel from the vehicle wheel speed signal outputted from the vehicle wheel speed detecting means; means provided in the learning means for learning a variation in the differential value calculated by the acceleration differential value calculating means, and for using a result of learning the variation in the differential value as the learning-resultant value representing the result of learning the variation in the vehicle wheel speed; and means provided in the road-surface condition detecting means for detecting the road-surface condition on the basis of a difference between the learning-resultant value and a variation in the differential value calculated by the acceleration differential value calculating means.
An eleventh aspect of this invention is based on the first aspect thereof, and provides an apparatus wherein the vehicle wheel speed detecting means comprises a vehicle wheel speed sensor.
A twelfth aspect of this invention provides an on-vehicle apparatus for detecting a condition of a road surface. The on-vehicle apparatus comprises first means for detecting a rotational speed of a vehicle wheel; second means for calculating an acceleration of the vehicle wheel from the vehicle-wheel speed detected by the first means; third means for periodically sampling the vehicle-wheel acceleration calculated by the second means to generate samples of the vehicle-wheel acceleration; fourth means for calculating a first variance among samples of the vehicle-wheel acceleration which are generated by the third means for a first time interval corresponding to current one revolution of the vehicle wheel, and calculating a second variance among samples of the vehicle-wheel acceleration which are generated by the third means for a second time interval corresponding to previous one revolution of the vehicle wheel; fifth means for calculating a difference between the first and second variances calculated by the fourth means; and sixth means for detecting a road-surface condition in response to the difference calculated by the fifth means.
A thirteenth aspect of this invention is based on the twelfth aspect thereof, and provides an on-vehicle apparatus wherein the sixth means comprises 1) seventh means for determining whether or not the difference calculated by the fifth means is smaller than a predetermined reference value, 2) eighth means for determining that the road-surface condition is good when the seventh means determines that the difference is smaller than the predetermined reference value, and 3) ninth means for determining that the road-surface condition is bad when the seventh means determines that the difference is not smaller than the predetermined reference value.
A fourteenth aspect of this invention provides an on-vehicle apparatus for detecting a condition of a road surface. The on-vehicle apparatus comprises first means for detecting a rotational speed of a vehicle wheel; second means for calculating an acceleration of the vehicle wheel from the vehicle-wheel speed detected by the first means; third means for periodically sampling the vehicle-wheel acceleration calculated by the second means to generate samples of the vehicle-wheel acceleration; fourth means for calculating a variance among samples of the vehicle-wheel acceleration which are generated by the third means for every time interval; fifth means for periodically calculating a first difference between two successive variances calculated by the fourth means; sixth means for periodically determining whether or not the first difference calculated by the fifth means is smaller than a predetermined reference value; seventh means for, only when the sixth means determines that the first difference is smaller than the predetermined reference value, defining a variance calculated by the fourth means and relating to the first difference as an effective reference; eighth means for generating a learning-resultant value in response to effective references generated by the seventh means; ninth means for calculating a second difference between a current variance calculated by the fourth means and the learning-resultant value generated by the eighth means; and tenth means for detecting a road-surface condition in response to the second difference calculated by the ninth means.
A fifteenth aspect of this invention is based on the fourteenth aspect thereof, and provides an on-vehicle apparatus wherein the tenth means comprises 1) eleventh means for determining whether or not the second difference calculated by the ninth means is smaller than a predetermined criterional value, 2) twelfth means for determining that the road-surface condition is good when the eleventh means determines that the second difference is smaller than the predetermined criterional value, and 3) thirteenth means for determining that the road-surface condition is bad when the eleventh means determines that the second difference is not smaller than the predetermined criterional value.